Various formulations of thermoplastic compositions have been developed in an attempt to at least partially replace non-degradable petroleum-based products with biodegradable components which can be used for the manufacture of extruded and/or molded articles such as films, utensils, containers and other packaging articles. Several of these compositions have been formulated which use starches such as a destructurized starch. Although starch compositions are biodegradable, they also tend to readily absorb moisture from humid air or by direct contact with water. This causes the moisture content of a molded article to increase and the article to lose its dimensional stability, and tear or collapse.
In an attempt to improve the structural stability of articles made from starch-based compositions, other ingredients have been included in the formulations. For example, compositions have been developed that include destructurized starch in combination with a water-insoluble synthetic thermoplastic polymer such as polyolefin or a polyester. Additionally, starches have been combined with protein to form starch-protein biopolymers that can provide moldable, biodegradable thermoplastics.
Modified cereal flours, such as pregelatinized or acid-modified corn flours, have been combined with a cross-linking compound such as glyoxal, to form a resinous material that may be used as a molding compound. A drawback of such compositions is that the lipids, fatty acids, and other minor components of the cereal flour can undergo an undesirable thermal reaction during processing that is detrimental to the strength and water-resistance of the molded article.
Therefore, an object of the invention is to provide a thermoplastic material that is thermally stable and can provide articles that have an increased level of physical strength and water-resistance, being capable of tolerating exposure to water over an extended period of time with minimal or no disintegration. It is a further object to provide a thermoplastic material that is biodegradable.